1. Field of the Invention
The present invention relates to a compressor and a method for manufacturing the same, and more particularly, to an easy method for manufacturing a swash plate and a variable capacity swash plate type compressor adopting the swash plate.
2. Description of the Related Art
In general, a compressor for use in an air conditioner for a vehicle pumps a heat exchange medium (refrigerant) in an evaporator by suctioning, compressing, and discharging a vaporized heat exchange medium.
A variety of compressors, such as swash plate, scroll, rotary, wobble plate, etc., which are classified according to the compression and driving methods, are available. The capacity of such compressors is fixed in the manufacture thereof. Thus, when such a compressor is used in an air conditioner for a vehicle operated by an engine, the load on the engine increases as the compressor operates because pumping capacity of the compressor cannot be varied in response to a cooling load.
To solve this problem, a variable capacity compressor having discharge capacity variable in response to the cooling load of the air conditioner has been suggested. An example of the variable capacity compressor is shown in FIG. 1. Referring to FIG. 1, a variable capacity swash plate type compressor includes a cylinder block 12 provided with a plurality of bores 11, a housing 13 combined with the cylinder block 12 to form a crank chamber 22 therein, a drive shaft 16 rotatably supported by the housing 13 and the cylinder block 12, a rotor or lug plate 17 mounted on the drive shaft 13 to be rotatable along with the drive shaft 16, and a swash plate 18. The swash plate 18 is hinged to the rotor 17 fixed on the drive shaft 16 by a hinge unit 19, and has a through hole 18a at the center through which the drive shaft 16 passes. Pistons 20 are disposed in each of the bores 11 and are engaged with the swash plate 18 via semi-spherical shoes 21.
The variable capacity swash plate type compressor having the structure described above pumps a compressed medium (refrigerant gas) by converting rotations of the rotor 17 and the swash plate 18, which rotates with the drive shaft 16, into reciprocation of the pistons 20. Here, the pumping rate of the variable capacity swash plate type compressor is varied depending on pumping load by adjusting the stroke of the pistons 20 with the swash plate 18 which is hinged to the rotor 17 and rotates at a predetermined inclination angle with respect to the rotor 17.
When the variable capacity swash plate type compressor is operated as described above, the swash plate 18 rotating together with the rotor 17 should be slidably guided along the drive shaft 16 through the through hole 18a formed at the center of the swash plate 18.
U.S. Pat. No. 5,699,716 discloses a swash plate having a through hole including first and second conical inner surfaces sloping inwards from each surface of the swash plate. In U.S. Pat. No. 5,125,803, a through hole in a cylindrical member has circular and conical inner surfaces to prevent undesired contact between the drive shaft and the cylindrical member during rotation of the cylindrical member. U.S. Pat. No. 4,846,049 discloses a cylindrical member having a hole with upper and lower planar surfaces having different angles relative to the central axis of the cylindrical member.
To form the through holes described above, the shapes of which are designed enable the swash plate or the cylindrical member to be displaced at both minimum and maximum inclination angles, at least two drillings and a single reaming are needed, thereby complicating the manufacture of the through hole with low productivity.
To solve the above-described problems, it is a first object of the present invention to provide a method for manufacturing a swash plate in which a through hole enabling the swash plate to be displaced at both maximum and minimum inclination angles without interference with a drive shaft is formed through a single process with improved productivity.
It is a second object of the present invention to provide a method for manufacturing a variable capacity swash plate type compressor with the swash plate.
To achieve the first object of the present invention, there is provided a method for manufacturing a swash plate or a hub having a boss formed by a through hole, the method comprising: (a) holding a swash plate or a hub in which a through hole is to be formed at a maximum inclination angle with respect to an horizontal axis; (b) calculating a diameter DH of the through hole using the relation DS less than DHxe2x89xa6(DS/cos xcex1)+1.0 mm, where DS is the diameter in millimeters of a drive shaft to be mounted passing through the through hole, and a is the maximum inclination angle of the swash plate; and (c) forming the through hole to have the diameter calculated in step (b) through a single process on the swash plate or the hub in a maximum inclination angle position, resulting in the boss of the swash plate or the hub, the single process being carried out in a direction parallel to the horizontal axis.
In step (c), it is preferable that the through hole is formed in a portion offset by a predetermined distance from the center of the swash plate or the hub.
It is preferable that step (b) comprises calculating a thickness (t) of the boss of the swash plate or the hub using the relation txe2x89xa62(axe2x88x92r)/tan xcex1, where a is the major axis in millimeters of elliptical openings of the through hole, and r is the radius in millimeters of the drive shaft.
To achieve the second object of the present invention, there is provided a variable capacity swash plate type compressor comprising: a cylinder block provided with a plurality of bores; front and rear housings combined with each other while the cylinder block is interposed therebetween to form a crank chamber and suction and discharge chambers; a drive shaft rotatably supported by the front and rear housings; a plurality of pistons reciprocally disposed in each of the bores of the cylinder block; a rotor fixedly mounted on the drive shaft to be rotatable with the drive shaft in the crank chamber; and a swash plate having a through hole and being hinged to the rotor by a hinge unit for reciprocating the plurality of pistons, the through hole through which the drive shaft passes, being formed through a single process to have a diameter DH satisfying the relation DS less than DHxe2x89xa6(DS/cos xcex1)+1.0 mm, where DS is the diameter of the drive shaft in millimeters, and xcex1 is the maximum inclination angle of the swash plate.